Study on mechanical properties of gas hydrate-bearing sediments under membrane boundary condition by DEM

Understanding the mechanical behavior of gas hydrate-bearing sediments (GHBS) is critical for safe hydrate extraction. This study employs the discrete element method (DEM) in PFC2D to investigate the macro- and meso-mechanical properties of GHBS. A novel layered staining technique is proposed to enhance deformation visualization in membrane-bound GHBS samples. Biaxial simulations were conducted on samples with varying hydrate saturations. Results demonstrate that the deviatoric stress–axial strain curves exhibit strength enhancement with increasing hydrate saturation, while volumetric strain–axial strain curves reveal distinct contraction-dilation behavior. Shear band formation observed during failure highlights the shear-dominated damage mechanism. At the mesoscale, key parameters—coordination number, deviatoric fabric, contact force, and particle rotation—were systematically analyzed. The coordination number initially increases and subsequently decreases with axial strain, correlating with the contraction-dilation transition. Similarly, deviatoric fabric and contact force evolution align with the hardening-softening characteristics of GHBS. Notably, intensified particle rotation within shear bands underscores its pivotal role in shear localization. These findings bridge mesoscopic mechanisms to macroscopic behavior, providing insights for optimizing hydrate extraction strategies.